In a hard disk drive for reading magnetic recording or content of record while rotating a hard disk at high speed, there is used a shaft-rotating type motor or such a shaft-fixed type motor as disclosed in U.S. Pat. No. 4,739,427.
The shaft-fixed type motor has, as shown in FIG. 15, a magnet 4 provided for a rotor 3 rotatably supported by a fixed shaft 1a through ball bearings 2a and 2b, and a stator winding 6 mounted on a stator core 5 so as to face the magnet 4, for rotationally driving hard disks 7 placed on the rotor 3 around the shaft center thereof.
Generally, the vibration proof characteristic has the following tendency:
When the number of revolutions increases, the vibration proof characteristic is deteriorated, and the vibration proof characteristic is also deteriorated even when a disk load is increased.
Naturally, this vibration proof characteristic will be improved if a motor resonance point is improved. Therefore, as described above, there is generally adopted a both ends supported structure in which a proximal end of the fixed shaft 1a is fixed to a lower case 8a and a tip end portion is fixed to an upper case 8b with a machine screw 9 to improve the resonance point, or in a cantilever supporting structure, a shaft diameter is generally made large.